p53 alterations in human leukemia-lymphoma cell lines: in vitroartifact or prerequisite for cell immortalization?

A framework for target discovery in rare cancers

While large-scale functional genetic screens have uncovered numerous cancer dependencies, rare cancers are poorly represented in such efforts and the landscape of dependencies in many rare cancers remains obscure. We performed genome-scale CRISPR knockout screens in an exemplar rare cancer, TFE3-translocation renal cell carcinoma (tRCC), revealing previously unknown tRCC-selective dependencies in pathways related to mitochondrial biogenesis, oxidative metabolism, and kidney lineage specification. To generalize to other rare cancers in which experimental models may not be readily available, we employed machine learning to infer gene dependencies in a tumor or cell line based on its transcriptional profile. By applying dependency prediction to alveolar soft part sarcoma (ASPS), a distinct rare cancer also driven by TFE3 translocations, we discovered and validated that MCL1 represents a dependency in ASPS but not tRCC. Finally, we applied our model to predict gene dependencies in tumors from the TCGA (11,373 tumors; 28 lineages) and multiple additional rare cancers (958 tumors across 16 types, including 13 distinct subtypes of kidney cancer), nominating potentially actionable vulnerabilities in several poorly-characterized cancer types. Our results couple unbiased functional genetic screening with a predictive model to establish a landscape of candidate vulnerabilities across cancers, including several rare cancers currently lacking in potential targets.

Comparison of primary and passaged tumor cell cultures and their application in personalized medicine

Passaged cell lines represent currently an integral component in various studies of malignant neoplasms. These cell lines are utilized for drug screening both in monolayer cultures or as part of three-dimensional (3D) tumor models. They can also be used to model the tumor microenvironment in vitro and in vivo through xenotransplantation into immunocompromised animals. However, immortalized cell lines have some limitations of their own. The homogeneity of cell line populations and the extensive passaging in monolayer systems make these models distant from the original disease. Recently, there has been a growing interest among scientists in the use of primary cell lines, as these are passaged directly from human tumor tissues. In this case, cells retain the morphological and functional characteristics of the tissue from which they were derived, an advantage often not observed in passaged cultures. This review highlights the advantages and limitations of passaged and primary cell cultures, their similarities and differences, as well as existing test systems that are based on primary and passaged cell cultures for drug screening purposes.

Distinct transcriptional programs stratify ovarian cancer cell lines into the five major histological subtypes

BACKGROUND

Epithelial ovarian cancer (OC) is a heterogenous disease consisting of five major histologically distinct subtypes: high-grade serous (HGSOC), low-grade serous (LGSOC), endometrioid (ENOC), clear cell (CCOC) and mucinous (MOC). Although HGSOC is the most prevalent subtype, representing 70-80% of cases, a 2013 landmark study by Domcke et al. found that the most frequently used OC cell lines are not molecularly representative of this subtype. This raises the question, if not HGSOC, from which subtype do these cell lines derive? Indeed, non-HGSOC subtypes often respond poorly to chemotherapy; therefore, representative models are imperative for developing new targeted therapeutics.

METHODS

Non-negative matrix factorisation (NMF) was applied to transcriptomic data from 44 OC cell lines in the Cancer Cell Line Encyclopedia, assessing the quality of clustering into 2-10 groups. Epithelial OC subtypes were assigned to cell lines optimally clustered into five transcriptionally distinct classes, confirmed by integration with subtype-specific mutations. A transcriptional subtype classifier was then developed by trialling three machine learning algorithms using subtype-specific metagenes defined by NMF. The ability of classifiers to predict subtype was tested using RNA sequencing of a living biobank of patient-derived OC models.

RESULTS

Application of NMF optimally clustered the 44 cell lines into five transcriptionally distinct groups. Close inspection of orthogonal datasets revealed this five-cluster delineation corresponds to the five major OC subtypes. This NMF-based classification validates the Domcke et al. analysis, in identifying lines most representative of HGSOC, and additionally identifies models representing the four other subtypes. However, NMF of the cell lines into two clusters did not align with the dualistic model of OC and suggests this classification is an oversimplification. Subtype designation of patient-derived models by a random forest transcriptional classifier aligned with prior diagnosis in 76% of unambiguous cases. In cases where there was disagreement, this often indicated potential alternative diagnosis, supported by a review of histological, molecular and clinical features.

CONCLUSIONS

This robust classification informs the selection of the most appropriate models for all five histotypes. Following further refinement on larger training cohorts, the transcriptional classification may represent a useful tool to support the classification of new model systems of OC subtypes.

Oncogenic WIP1 phosphatase attenuates the DNA damage response and sensitizes p53 mutant Jurkat cells to apoptosis

Wild-type (wt) p53-induced phosphatase 1 (Wip1), encoded by the protein phosphatase, Mg²⁺/Mn²⁺ dependent 1D (PPM1D) gene, is a serine/threonine phosphatase induced upon genotoxic stress in a p53-dependent manner. Wip1/PPM1D is frequently overexpressed, amplified and mutated in human solid tumors harboring wt p53 and is thus currently recognized as an oncogene. Oncogenic Wip1 dampens cellular stress responses, such as cell cycle checkpoints, apoptosis and senescence, and consequently increases resistance to anticancer therapeutics. Targeting Wip1 has emerged as a therapeutic strategy for tumors harboring wt p53. However, little is known about the efficacy of Wip1-targeted therapies in tumors lacking p53. The present study aimed to investigate the potential role of oncogenic Wip1 in p53 mutant (mt) Jurkat cells. In the present study, it was demonstrated that p53 mt Jurkat cells exhibited PPM1D/Wip1 gene amplification and expressed relatively high levels of Wip1, as confirmed by gene copy number and RNA expression analysis. In addition, Jurkat cells underwent G2 cell cycle arrest, apoptotic cell death and senescence in response to etoposide and doxorubicin, although the phosphorylation levels of DNA damage response (DDR) elements, including ataxia-telangiectasia mutated, ataxia-telangiestasia and Rad3-related, checkpoint kinase (Chk)1 and Chk2 were significantly low. Accordingly, the targeting of Wip1 phosphatase by RNA interference increased the phosphorylation of DDR elements, but decreased the rate of apoptosis in response to etoposide or doxorubicin in Jurkat cells. The induction of senescence or cell cycle arrest was not affected by the knockdown of Wip1. The results suggest that increased Wip1 expression enhances the apoptotic sensitivity of Jurkat cells in response to chemotherapeutic agents by attenuating DDR signaling. The present study highlights the possible pro-apoptotic role of Wip1 in a p53 mt T-cell acute lymphoblastic leukemia cell line. The data suggest the careful consideration of future treatment strategies aiming to manipulate or target Wip1 in human cancers lacking p53.

A first-generation pediatric cancer dependency map

Exciting therapeutic targets are emerging from CRISPR-based screens of high mutational-burden adult cancers. A key question, however, is whether functional genomic approaches will yield new targets in pediatric cancers, known for remarkably few mutations, which often encode proteins considered challenging drug targets. To address this, we created a first-generation pediatric cancer dependency map representing 13 pediatric solid and brain tumor types. Eighty-two pediatric cancer cell lines were subjected to genome-scale CRISPR-Cas9 loss-of-function screening to identify genes required for cell survival. In contrast to the finding that pediatric cancers harbor fewer somatic mutations, we found a similar complexity of genetic dependencies in pediatric cancer cell lines compared to that in adult models. Findings from the pediatric cancer dependency map provide preclinical support for ongoing precision medicine clinical trials. The vulnerabilities observed in pediatric cancers were often distinct from those in adult cancer, indicating that repurposing adult oncology drugs will be insufficient to address childhood cancers.

Novel patient-derived preclinical models of liver cancer

Preclinical models of cancer based on the use of human cancer cell lines and mouse models have enabled discoveries that have been successfully translated into patients. And yet the majority of clinical trials fail, emphasising the urgent need to improve preclinical research to better interrogate the potential efficacy of each therapy and the patient population most likely to benefit. This is particularly important for liver malignancies, which lack highly efficient treatments and account for hundreds of thousands of deaths around the globe. Given the intricate network of genetic and environmental factors that contribute to liver cancer development and progression, the identification of new druggable targets will mainly depend on establishing preclinical models that mirror the complexity of features observed in patients. The development of new 3D cell culture systems, originating from cells/tissues isolated from patients, might create new opportunities for the generation of more specific and personalised therapies. However, these systems are unable to recapitulate the tumour microenvironment and interactions with the immune system, both proven to be critical influences on therapeutic outcomes. Patient-derived xenografts, in particular with humanised mouse models, more faithfully mimic the physiology of human liver cancer but are costly and time-consuming, which can be prohibitive for personalising therapies in the setting of an aggressive malignancy. In this review, we discuss the latest advances in the development of more accurate preclinical models to better understand liver cancer biology and identify paradigm-changing therapies, stressing the importance of a bi-directional communicative flow between clinicians and researchers to establish reliable model systems and determine how best to apply them to expanding our current knowledge.

Human primary liver cancer-derived organoid cultures for disease modeling and drug screening

Human liver cancer research currently lacks in vitro models that can faithfully recapitulate the pathophysiology of the original tumor. We recently described a novel, near-physiological organoid culture system, wherein primary human healthy liver cells form long-term expanding organoids that retain liver tissue function and genetic stability. Here we extend this culture system to the propagation of primary liver cancer (PLC) organoids from three of the most common PLC subtypes: hepatocellular carcinoma (HCC), cholangiocarcinoma (CC) and combined HCC/CC (CHC) tumors. PLC-derived organoid cultures preserve the histological architecture, gene expression and genomic landscape of the original tumor, allowing for discrimination between different tumor tissues and subtypes, even after long-term expansion in culture in the same medium conditions. Xenograft studies demonstrate that the tumorogenic potential, histological features and metastatic properties of PLC-derived organoids are preserved in vivo. PLC-derived organoids are amenable for biomarker identification and drug-screening testing and led to the identification of the ERK inhibitor SCH772984 as a potential therapeutic agent for primary liver cancer. We thus demonstrate the wide-ranging biomedical utilities of PLC-derived organoid models in furthering the understanding of liver cancer biology and in developing personalized-medicine approaches for the disease.

Establishment and genomic characterization of primary salivary duct carcinoma cell line

OBJECTIVES

To develop and characterize in vitro salivary duct carcinoma as a surrogate for functional studies.

MATERIALS AND METHODS

Cells were dispersed from tumor tissue fragments under sterile conditions in RPMI media. Disassociated cells were cultivated, immortalized with hTERT and propagated for more than 100 passages. Morphologic, linage, cytogenetic and genomic analyses were performed on different passages of cell line and primary tumor. Soft agar growth was performed.

RESULTS

Analysis of cytomorphologic features, growth characteristics and lineage specific markers expression confirmed the epithelial derivation and the neoplastic nature of the cell line. DNA STRs analysis showed identical match of both cell line and primary tumor. Cultivated cells expressed Androgen Receptor (AR), PTEN, and EFGR proteins and the AR-V7 isoform transcript. Comparative exome-sequencing identified common mutated genes in both cell line and primary tumor. In-vitro colony formation of late passages is established.

CONCLUSION

We report the development of the first human salivary duct carcinoma cell line (MDA-SDC-04) that retains critical biological and genomic features of the donor tumor.

Hepatocellular carcinoma cell lines retain the genomic and transcriptomic landscapes of primary human cancers

Hepatocellular carcinoma (HCC) cell lines are useful in vitro models for the study of primary HCCs. Because cell lines acquire additional mutations in culture, it is important to understand to what extent HCC cell lines retain the genetic landscapes of primary HCCs. Most HCC cell lines were established during the last century, precluding comparison between cell lines and primary cancers. In this study, 9 Chinese HCC cell lines with matched patient-derived cells at low passages (PDCs) were established in the defined culture condition. Whole genome analyses of 4 HCC cell lines showed that genomic mutation landscapes, including mutations, copy number alterations (CNAs) and HBV integrations, were highly stable during cell line establishment. Importantly, genetic alterations in cancer drivers and druggable genes were reserved in cell lines. HCC cell lines also retained gene expression patterns of primary HCCs during in vitro culture. Finally, sequential analysis of HCC cell lines and PDCs at different passages revealed their comparable and stable genomic and transcriptomic levels if maintained within proper passages. These results show that HCC cell lines largely retain the genomic and transcriptomic landscapes of primary HCCs, thus laying the rationale for testing HCC cell lines as preclinical models in precision medicine.

Thioimidazoline based compounds reverse glucocorticoid resistance in human acute lymphoblastic leukemia xenografts

Glucocorticoids form a critical component of chemotherapy regimens for pediatric acute lymphoblastic leukemia (ALL) and the initial response to glucocorticoid therapy is a major prognostic factor, where resistance is predictive of poor outcome. A high-throughput screen identified four thioimidazoline-containing compounds that reversed dexamethasone resistance in an ALL xenograft derived from a chemoresistant pediatric ALL. The lead compound (1) was synergistic when used in combination with the glucocorticoids, dexamethasone or prednisolone. Synergy was observed in a range of dexamethasone-resistant xenografts representative of B-cell precursor ALL (BCP-ALL) and T-cell ALL. We describe here the synthesis of twenty compounds and biological evaluation of thirty two molecules that explore the structure-activity relationships (SAR) of this novel class of glucocorticoid sensitizing compounds. SAR analysis has identified that the most effective dexamethasone sensitizers contain a thioimidazoline acetamide substructure with a large hydrophobic moiety on the acetamide.

Establishment and characterization of a rare atypical chronic myeloid leukemia cell line NT-1

Human leukemia cell lines are of great value in leukemia research. In this study, we established and described the biological characteristics of a rare atypical chronic myeloid (aCML) leukemia cell line (NT-1). Mononuclear cells were isolated from the bone marrow of a patient with atypical chronic myeloid leukemia (Ph(-)/bcr(-)/abl(-)), and were passaged by liquid culture. Cells were maintained without any cytokines for over 1 year, and named NT-1. This cell line was extensively characterized using morphological assays, flow cytometry, cytogenetic analysis, clonogenic culture, quantitative fluorescent PCR, short tandem repeating sequence PCR (STR-PCR) and array-CGH. Its tumorigenic capacity was also examined in nude mice. The NT-1 cell line had morphological features of chronic myeloid leukemia and major myeloid markers (CD13, CD33, CD11b). Additionally, NT-1 expressed progenitor cells and natural killer cell-related antigens such as CD34, CD117, CD56. Cytogenetic analysis initially demonstrated two abnormalities: 47, xx, +8 and 47, xx, +8 accompanied by t(5;12)(q31;p13) translocation. The one-year passage process did not alter the karyotype. NT-1 cells maintained the same morphology, immunophenotyping and cytogenetic features as primary leukemia cells, which was strongly supported by STR-PCR results. Neither Epstein-Barr virus nor mycoplasma was detected in the NT-1 line. In addition, NT-1 cells showed high tumorigenic capacity in nude mice. NT-1 is a new atypical chronic myeloid leukemia cell line with the +8 and t(5,12) translocation, and exhibits high tumorigenicity in nude mice. This new cell line provides a useful tool for the study of leukemogenesis.

Analysis of TP53 mutation status in human cancer cell lines: a reassessment

Tumor-derived cell lines play an important role in the investigation of tumor biology and genetics. Across a wide array of studies, they have been tools of choice for the discovery of important genes involved in cancer and for the analysis of the cellular pathways that are impaired by diverse oncogenic events. They are also invaluable for screening novel anticancer drugs. The TP53 protein is a major component of multiple pathways that regulate cellular response to various types of stress. Therefore, TP53 status affects the phenotype of tumor cell lines profoundly and must be carefully ascertained for any experimental project. In the present review, we use the 2014 release of the UMD TP53 database to show that TP53 status is still controversial for numerous cell lines, including some widely used lines from the NCI-60 panel. Our analysis clearly confirms that, despite numerous warnings, the misidentification of cell lines is still present as a silent and neglected issue, and that extreme care must be taken when determining the status of p53, because errors may lead to disastrous experimental interpretations. A novel compendium gathering the TP53 status of 2,500 cell lines has been made available (http://p53.fr). A stand-alone application can be used to browse the database and extract pertinent information on cell lines and associated TP53 mutations. It will be updated regularly to minimize any scientific issues associated with the use of misidentified cell lines (http://p53.fr).

Non-Hodgkin's B-cell lymphoma: advances in molecular strategies targeting drug resistance

Non-Hodgkin's lymphoma (NHL) is a heterogeneous class of cancers displaying a diverse range of biological phenotypes, clinical behaviours and prognoses. Standard treatments for B-cell NHL are anthracycline-based combinatorial chemotherapy regimens composed of cyclophosphamide, doxorubicin, vincristine and prednisolone. Even though complete response rates of 40-50% with chemotherapy can be attained, a substantial proportion of patients relapse, resulting in 3-year overall survival rates of about 30%. Relapsed lymphomas are refractory to subsequent treatments with the initial chemotherapy regimen and can exhibit cross-resistance to a wide variety of anticancer drugs. The emergence of acquired chemoresistance thus poses a challenge in the clinic preventing the successful treatment and cure of disseminated B-cell lymphomas. Gene-expression analyses have increased our understanding of the molecular basis of chemotherapy resistance and identified rational targets for drug interventions to prevent and treat relapsed/refractory diffuse large B-cell lymphoma. Acquisition of drug resistance in lymphoma is in part driven by the inherent genetic heterogeneity and instability of the tumour cells. Due to the genetic heterogeneity of B-cell NHL, many different pathways leading to drug resistance have been identified. Successful treatment of chemoresistant NHL will thus require the rational design of combinatorial drugs targeting multiple pathways specific to different subtypes of B-cell NHL as well as the development of personalized approaches to address patient-to-patient genetic heterogeneity. This review highlights the new insights into the molecular basis of chemorefractory B-cell NHL that are facilitating the rational design of novel strategies to overcome drug resistance.

In Vivo RNAi screening identifies a leukemia-specific dependence on integrin beta 3 signaling

We used an in vivo small hairpin RNA (shRNA) screening approach to identify genes that are essential for MLL-AF9 acute myeloid leukemia (AML). We found that Integrin Beta 3 (Itgb3) is essential for murine leukemia cells in vivo and for human leukemia cells in xenotransplantation studies. In leukemia cells, Itgb3 knockdown impaired homing, downregulated LSC transcriptional programs, and induced differentiation via the intracellular kinase Syk. In contrast, loss of Itgb3 in normal hematopoietic stem and progenitor cells did not affect engraftment, reconstitution, or differentiation. Finally, using an Itgb3 knockout mouse model, we confirmed that Itgb3 is dispensable for normal hematopoiesis but is required for leukemogenesis. Our results establish the significance of the Itgb3 signaling pathway as a potential therapeutic target in AML.

Molecular approaches towards development of purified natural products and their structurally known derivatives as efficient anti-cancer drugs: current trends

Several natural products and their derivatives, either in purified or structurally identified form, exhibit immense pharmacological and biological properties, some of them showing considerable anticancer potential. Although the molecular mechanisms of action of some of these products are yet to be elucidated, extensive research in this area continues to generate new data that are clinically exploitable. Recent advancement in molecular biology, high throughput screening, biomarker identifications, target selection and genomic approaches have enabled us to understand salient interactions of natural products and their derivatives with cancer cells vis-à-vis normal cells. In this review we highlight the recent approaches and application of innovative technologies made to improve quality as well as efficiency of structurally identified natural products and their derivatives, particularly in small molecular forms capable of being used in "targeted therapies" in oncology. These products preferentially involve multiple mechanistic pathways and overcome chemo-resistance in tumor types with cumulative action. We also mention briefly a few physico-chemical features that compare natural products with drugs in recent natural product discovery approaches. We further report here a few purified natural products as examples that provide molecular interventions in cancer therapeutics to give the reader a glimpse of the current trends of approach for discovering useful anticancer drugs.

Restoration of microRNA-214 expression reduces growth of myeloma cells through positive regulation of P53 and inhibition of DNA replication

MicroRNA have been demonstrated to be deregulated in multiple myeloma. We have previously reported that miR-214 is down-regulated in multiple myeloma compared to in normal plasma cells. The functional role of miR-214 in myeloma pathogenesis was explored by transfecting myeloma cell lines with synthetic microRNA followed by gene expression profiling. Putative miR-214 targets were validated by luciferase reporter assay. Ectopic expression of miR-214 reduced cell growth and induced apoptosis of myeloma cells. In order to identify the potential direct target genes of miR-214 which could be involved in the biological pathways regulated by this microRNA, gene expression profiling of the H929 myeloma cell line transfected with precursor miR-214 was carried out. Functional analysis revealed significant enrichment for DNA replication, cell cycle phase and DNA binding. miR-214 directly down-regulated the expression of PSMD10, which encodes the oncoprotein gankyrin, and ASF1B, a histone chaperone required for DNA replication, by binding to their 3'-untranslated regions. In addition, gankyrin inhibition induced an increase of P53 mRNA levels and subsequent up-regulation of CDKN1A (p21Waf1/Cip1) and BAX transcripts, which are direct transcriptional targets of p53. In conclusion, MiR-214 functions as a tumor suppressor in myeloma by positive regulation of p53 and inhibition of DNA replication.

Glucocorticoid resistance in paediatric acute lymphoblastic leukaemia

Glucocorticoids (GCs), such as prednisolone and dexamethasone, are key components in multi-agent chemotherapy protocols used for the treatment of acute lymphoblastic leukaemia (ALL). Approximately 10% of children with ALL will respond poorly to GCs, and GC resistance is associated with a significantly inferior outcome. This review summarises the current knowledge of GC resistance in ALL, including the roles of the GC receptor and its co-chaperone molecules, the pro-apoptotic and pro-survival B-cell lymphoma 2 family members and alternative non-apoptotic mechanisms of cell death. It concludes with a discussion on therapeutic attempts to overcome GC resistance.

Establishment and characterization of a new human acute myelomonocytic leukemia cell line JIH-3

Here, a new acute myelomonocytic leukemia (AMML) cell line, JIH-3, is reported, and its biological characteristics are described. JIH-3 cells were maintained without any cytokines for 27 months. The JIH-3 cell line showed typical myelomonocytic morphological features. Additionally, it mainly expressed myeloid and monocytic markers (CD13, CD14, CD11b, CD15 and CD33), although it also expressed other antigens such as the markers of T and B lymphocytic lineage as well as stem cell, progenitor cell, and natural killer cell-related antigens (CD4, CD5, CD7, CD10, CD22, CD34, CD38, HLADR, CD16/CD56 and CD56); the expression of these markers, suggested that this cell line was in the early stage of myelomonocytic differentiation. Cytogenetic analysis initially showed a karyotype of 46, XY, del(7) (p1?3p2?2). During the passage period, the cells with this karyotype gradually decreased and were replaced by cells with a 45,XY,dic(4;7)(p11;p11),del(15)(q2?2) karyotype. Chromosome painting showed a deletion in the short arm of chromosome 7 for del(7)(p1?3p2?2) and der(4;7)(p11;p11). The latter had larger deleted segment than the former. Fluorescence in situ hybridization (FISH) revealed the dicentric nature of der(4;7), and Multiplex FISH (M-FISH) confirmed that der(4;7) was an unbalanced translocation. A deletion involving the 7p region on dic(4;7)(p11;p11) harbors many genes, including CDC2L5, C7ORF11, C7ORF10 and INHBA. Haploinsufficiency of the genes on 4p, 7p and 15q caused by deletions of 4p, 7p and 15q2?2 that resulted from dic(4;7)(p11;p11) and del(15)(q2?2) may play important roles in leukemogenesis and in the establishment of the JIH-3 cell line. JIH-3 cells did not express multidrug resistance (MDR)-related genes and apoptosis-related genes such as MDR1, multidrug resistance-related protein, lung resistance protein, BCL-2, Bax, GS-π or Fax, only P21 expression was detected, which probably leads the MDR indirectly through inhibition of the activities of cyclin-dependent kinase (CDK). JIH-3 cells had tumorigenic capacity in nude mice. In conclusion, JIH-3 is a new acute myelomonocytic leukemia cell line. It is from a well-characterized background and provides a new useful tool for the study of leukemia patients with a 7p deletion.

Evaluation of the NOD/SCID xenograft model for glucocorticoid-regulated gene expression in childhood B-cell precursor acute lymphoblastic leukemia

Background

Glucocorticoids such as prednisolone and dexamethasone are critical drugs used in multi-agent chemotherapy protocols used to treat acute lymphoblastic leukemia (ALL), and response to glucocorticoids is highly predictive of outcome. The NOD/SCID xenograft mouse model of ALL is a clinically relevant model in which the mice develop a systemic leukemia which retains the fundamental biological characteristics of the original disease. Here we report a study evaluating the NOD/SCID xenograft mouse model to investigate glucocorticoid-induced gene expression. Cells from a glucocorticoid-sensitive xenograft derived from a child with B-cell precursor ALL were inoculated into NOD/SCID mice. When highly engrafted the mice were randomized into groups of 4 to receive dexamethasone 15 mg/kg by intraperitoneal injection or vehicle control. Leukemia cells were harvested from mice spleens at 0, 8, 24 or 48 hours thereafter, and gene expression analyzed on Illumina WG-6_V3 chips, comparing all groups to time 0 hours.

Results

The 8 hour dexamethasone-treated timepoint had the highest number of significantly differentially expressed genes, with fewer observed at the 24 and 48 hour timepoints, and with minimal changes seen across the time-matched controls. When compared to publicly available datasets of glucocorticoid-induced gene expression from an in vitro cell line study and from an in vivo study of patients with ALL, at the level of pathways, expression changes in the 8 hour xenograft samples showed a similar response to patients treated with glucocorticoids. Replicate analysis revealed that at the 8 hour timepoint, a dataset with high signal and differential expression, using data from 3 replicates instead of 4 resulted in excellent recovery scores of > 0.9. However at other timepoints with less signal very poor recovery scores were obtained with 3 replicates.

Conclusions

The NOD/SCID xenograft mouse model provides a reproducible experimental system in which to investigate clinically-relevant mechanisms of drug-induced gene regulation in ALL; the 8 hour timepoint provides the highest number of significantly differentially expressed genes; time-matched controls are redundant and excellent recovery scores can be obtained with 3 replicates.

The ups and downs of p53 regulation in hematopoietic stem cells

Hematopoietic stem cells provide an indispensible source for replenishing the blood with all its constituents throughout the organism's lifetime. Mice with a compromised hematopoietic stem cell compartment cannot survive. p53, a major tumor suppressor gene, has been implicated in regulation of hematopoiesis. In particular, p53 plays a role in homeostasis by regulating HSC quiescence and self renewal. We recently utilized a hypomorphic p53(515C) allele in conjunction with Mdm2, a negative regulator of p53 to gain insights into the role of p53 in hematopoietic regulation. Our analyses revealed that p53(515C/515C) Mdm2(-/-) double mutant mice die soon after birth due to hematopoietic failure. Further mechanistic studies revealed that in the absence of Mdm2, ROS induced postnatal p53 activity depletes hematopoietic stem cells, progenitors and differentiated cells.

Dysregulated microRNAs affect pathways and targets of biologic relevance in nasal-type natural killer/T-cell lymphoma

We performed a comprehensive genome-wide miRNA expression profiling of extranodal nasal-type natural killer/T-cell lymphoma (NKTL) using formalin-fixed paraffin-embedded tissue (n = 30) and NK cell lines (n = 6) compared with normal NK cells, with the objective of understanding the pathogenetic role of miRNA deregulation in NKTL. Compared with normal NK cells, differentially expressed miRNAs in NKTL are predominantly down-regulated. Re-expression of down-regulated miRNAs, such as miR-101, miR-26a, miR26b, miR-28-5, and miR-363, reduced the growth of the NK cell line and modulated the expression of their predicted target genes, suggesting the potential functional role of the deregulated miRNAs in the oncogenesis of NKTL. Taken together, the predicted targets whose expression is inversely correlated with the expression of deregulated miRNA in NKTL are significantly enriched for genes involved in cell cycle-related, p53, and MAPK signaling pathways. We also performed immunohistochemical validation for selected target proteins and found overexpression of MUM1, BLIMP1, and STMN1 in NKTL, and notably, a corresponding increase in MYC expression. Because MYC is known to cause repression of miRNA expression, it is possible that MYC activation in NKTL may contribute to the suppression of the miRNAs regulating MUM1, BLIMP1, and STMN1.

Establishment and culture of leukemia-lymphoma cell lines

The advent of continuous human leukemia-lymphoma cell lines as a rich resource of abundant, accessible, and manipulable living cells has contributed significantly to a better understanding of the pathophysiology of hematopoietic tumors. The first leukemia-lymphoma cell lines were established in 1963 and since then large numbers of new cell lines have been described. The major advantages of continuous leukemia-lymphoma cell lines are the unlimited supply and worldwide availability of identical cell material and the infinite viable storability in liquid nitrogen. These cell lines are characterized generally by monoclonal origin and differentiation arrest, sustained proliferation in vitro under preservation of most cellular features, and by specific genetic alterations. Here some of the more promising techniques for establishing new leukemia-lymphoma cell lines and the basic principles for culturing these cells are described. Several clinical and cell culture parameters might have some influence on the success rate, e.g., choice of culture medium and culture conditions, specimen site of the primary cells, and status of the patient at the time of sample collection.

History of leukemia-lymphoma cell lines

We outline the near 50-year history of leukemia-lymphoma (LL) cell lines - a key model system in biomedicine. Due to the detailed documentation of their oncogenomic and transcriptional alterations via recent advances in molecular medicine, LL cell lines may be fitted to parent tumors with a degree of precision unattainable in other cancers. We have surveyed the corpus of published LL cell lines and found 637 examples that meet minimum standards of authentication and characterization. Alarmingly, the rate of establishment of new LL cell lines has plummeted over the last decade. Although the main hematopoietic developmental cell types are represented by cell lines, some LL categories stubbornly resist establishment in vitro. The advent of engineering techniques for immortalizing primary human cells that maintain differentiation means the time is ripe for renewed search for in vitro models from un(der)represented hematologic entities. Given their manifold applications in biomedicine, there is little doubt that LL-derived cell lines will continue to play a vital part well into the next half-century as well.

Cell line-based platforms to evaluate the therapeutic efficacy of candidate anticancer agents

Efforts to discover new cancer drugs and predict their clinical activity are limited by the fact that laboratory models to test drug efficacy do not faithfully recapitulate this complex disease. One important model system for evaluating candidate anticancer agents is human tumour-derived cell lines. Although cultured cancer cells can exhibit distinct properties compared with their naturally growing counterparts, recent technologies that facilitate the parallel analysis of large panels of such lines, together with genomic technologies that define their genetic constitution, have revitalized efforts to use cancer cell lines to assess the clinical utility of new investigational cancer drugs and to discover predictive biomarkers.

The Bcl-2 homology domain 3 mimetic ABT-737 targets the apoptotic machinery in acute lymphoblastic leukemia resulting in synergistic in vitro and in vivo interactions with established drugs

Antiapoptotic Bcl-2 proteins are overexpressed in a number of cancers, including leukemias, and are frequently associated with resistance to conventional chemotherapeutic drugs. ABT-737, a Bcl-2 homology domain 3 mimetic (for structure, see Nature 435:677-681, 2005) inhibits the prosurvival function of Bcl-2, Bcl-X(L), and Bcl-w. We show that ABT-737 was effective as a single agent against a panel of pediatric acute lymphoblastic leukemia (ALL) xenografts, previously established, from patient biopsies, in immunodeficient mice. Although in vitro resistance of leukemia cell lines correlated with expression of the prosurvival protein Mcl-1, there was no relationship between Mcl-1 expression and in vivo xenograft response to ABT-737. However, expression of the pro-apoptotic protein Bim, and the extent of its association with Bcl-2, significantly correlated with in vivo ABT-737 sensitivity. ABT-737 potentiated the antileukemic effects of L-asparaginase, topotecan, vincristine, and etoposide against drug-resistant xenografts in vitro and in vivo. Finally, we show that the combination of L-asparaginase (by specifically down-regulating Mcl-1 protein levels), topotecan (by activating p53 via DNA damage), and ABT-737 (by inhibiting antiapoptotic Bcl-2 family members) caused profound synergistic antileukemic efficacy both in vitro and in vivo. Rational targeting of specific components of the apoptotic pathway may be a useful approach to improve the treatment of refractory or relapsed pediatric ALL. Overall, this study supports the inclusion of the clinical derivative of ABT-737, ABT-263 (for structure, see Cancer Res 68:3421-3428, 2008), into clinical trials against relapsed/refractory pediatric ALL.

Differences in the Expression of Apoptotic Proteins in Burkitt's Lymphoma Cell Lines: Potential Models for Screening Apoptosis-Inducing Agents

Mammalian cells undergo programmed cell death by orchestrated interactions involving multiple independent pathways. At least one of them, the p53-dependent pathway is commonly compromised in Burkitt's lymphoma (BL) cell lines. Differences in the integrity of this pathway in various BL cell lines have made them useful experimental models in understanding response to standard or novel antitumor drugs vis-a-vis the p53 pathway. Non-p53-dependent loss of apoptotic regulation also contributes to the genesis and/or progression of lymphomas and it is possible that BL cell lines also represent these models. We have characterized the expression of multiple apoptotic proteins in a panel of BL cell lines and describe cell lines with loss of cIAP1, cIAP2, Bax, Bak, Bcl-Xs and p38 MAP-kinase. This data should make this panel of cell lines a useful screening system for testing novel apoptotic inducers.

Schedule-dependent synergy between the heat shock protein 90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin and doxorubicin restores apoptosis to p53-mutant lymphoma cell lines

PURPOSE

Loss of p53 function impairs apoptosis induced by DNA-damaging agents used for cancer therapy. Here, we examined the effect of the heat shock protein 90 (HSP90) inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (DMAG) on doxorubicin-induced apoptosis in lymphoma. We aimed to establish the optimal schedule for administration of both drugs in combination and the molecular basis for their interaction.

EXPERIMENTAL DESIGN

Isogenic lymphoblastoid and nonisogenic lymphoma cell lines differing in p53 status were exposed to each drug or combination. Drug effects were examined using Annexin V, active caspase-3, cell cycle, and cytotoxicity assays. Synergy was evaluated by median effect/combination index. Protein expression and kinase inhibition provided insight into the molecular mechanisms of drug interaction.

RESULTS

Presence of mutant p53 conferred increased survival to single agents. Nevertheless, DMAG showed synergistic toxicity with doxorubicin independently of p53 status. Synergy required exposure to doxorubicin before DMAG. DMAG-mediated down-regulation of CHK1, a known HSP90 client, forced doxorubicin-treated cells into premature mitosis followed by apoptosis. A CHK1 inhibitor, SB-218078, reproduced the effect of DMAG. Administration of DMAG before doxorubicin resulted in G1-S arrest and protection from apoptosis, leading to additive or antagonistic interactions that were exacerbated by p53 mutation.

CONCLUSIONS

Administration of DMAG to doxorubicin-primed cells induced premature mitosis and had a synergistic effect on apoptosis regardless of p53 status. These observations provide a rationale for prospective clinical trials and stress the need to consider schedule of exposure as a critical determinant of the overall response when DMAG is combined with chemotherapeutic agents for the treatment of patients with relapsed/refractory disease.

In utero Exposure of Mice to Dibenzo[a,l]Pyrene Produces Lymphoma in the Offspring: Role of the Aryl Hydrocarbon Receptor

Lymphoma and leukemia are the most common cancers in children and young adults; in utero carcinogen exposure may contribute to the etiology of these cancers. A polycyclic aromatic hydrocarbon (PAH), dibenzo[a,l]pyrene (DBP), was given to pregnant mice (15 mg/kg body weight, gavage) on gestation day 17. Significant mortalities in offspring, beginning at 12 weeks of age, were observed due to an aggressive T-cell lymphoblastic lymphoma. Lymphocytes invaded numerous tissues. All mice surviving 10 months, exposed in utero to DBP, exhibited lung tumors; some mice also had liver tumors. To assess the role of the aryl hydrocarbon receptor (AHR) in DBP transplacental cancer, B6129SF1/J (AHR(b-1/d), responsive) mice were crossed with strain 129S1/SvIm (AHR(d/d), nonresponsive) to determine the effect of maternal and fetal AHR status on carcinogenesis. Offspring born to nonresponsive mothers had greater susceptibility to lymphoma, irrespective of offspring phenotype. However, when the mother was responsive, an AHR-responsive phenotype in offspring increased mortality by 2-fold. In DBP-induced lymphomas, no evidence was found for TP53, beta-catenin, or Ki-ras mutations but lung adenomas of mice surviving to 10 months of age had mutations in Ki-ras codons 12 and 13. Lung adenomas exhibited a 50% decrease and a 35-fold increase in expression of Rb and p19/ARF mRNA, respectively. This is the first demonstration that transplacental exposure to an environmental PAH can induce a highly aggressive lymphoma in mice and raises the possibility that PAH exposures to pregnant women could contribute to similar cancers in children and young adults.

Inhibition of leukemic cell growth by a novel anti-cancer drug (GUT-70) from calophyllum brasiliense that acts by induction of apoptosis

During our search for cancer chemopreventing compounds derived from plant sources, we discovered that the natural product GUT-70, isolated from the stem bark of Calophyllum brasiliense collected in Brazil, significantly inhibits the growth of leukemic cells. GUT-70, characterized as a tricyclic coumarin, 5-methoxy-2,2-dimethyl-6-(2-methyl-1-oxo-2-butenyl) -10-propyl-2H,8H-benzo[1,2-b;3,4-b']dipyran-8-one (C(23)H(26)O(5)), inhibited all 6 human leukemic cell lines evaluated, including the P-glycoprotein overexpressing cell line, in a concentration and time-dependent manner with IC(50) values from 2-5 microM. Furthermore, GUT-70 did not inhibit colony formation by normal hematopoietic progenitors up to 30 microM and also did not inhibit the proliferation of normal human hepatocytes up to 30 microM. GUT-70 activated the caspase 2, 3, 8 and 9, and induced the apoptosis in leukemic cells, which was inhibited by caspase inhibitors. GUT-70 induced anti-leukemic effects independent of the p53-p2l(WAFl/CIP1) pathway and increased the overall expression of p27(KIP1) and p57(KIP2), to stop the cell cycle at the G(1)/S transition. Thus, a novel anti-cancer drug, GUT-70 isolated from the stem bark of C. brasiliense induces caspase-mediated and p53-independent apoptosis to overcome multidrug resistance and may become a potent leukemia therapeutics.

TP53 in hematological cancer: low incidence of mutations with significant clinical relevance

Inactivation of the wild-type p53 gene (TP53) by various genetic alterations is a major event in human tumorigenesis. More than 60% of human primary tumors exhibit a mutation in the p53 gene. Hematological malignancies present a rather low incidence of genetic alterations in this gene (10-20%). Nevertheless, epidemiological studies of the hematological malignancies indicate that the prognosis of patients with a mutation in the p53 gene is worse than those expressing the wild-type p53 protein. Correlations between drug resistance, altered apoptosis, and mutations in the p53 gene are found in hematological malignancies and leukemias. These issues, as well as the possibility of exploiting p53 and its various functions for new therapeutic strategies, are discussed in the present review.

Apoptosis or growth arrest: modulation of the cellular response to p53 by proliferative signals

Activation of the tumor suppressor p53 after genotoxic insults may result in two different responses: growth arrest or apoptosis. In this study, we analysed how mitogenic stimulation of primary mouse lymphocytes influences p53 signaling upon gamma-irradiation. We found that G(0) lymphocytes rapidly went into p53-dependent apoptosis, whereas stimulated lymphocytes went into a p53-dependent, p21-mediated growth arrest. The switch in p53 response upon stimulation did neither result from a switch in transcriptional activation of major p53 target genes, nor from the high level of p21 expressed in stimulated, irradiated cells. Growth stimulation, however, led to the upregulation of the antiapoptotic factors Bcl-x(L) and Bfl-1. In resting cells, p53 induced apoptosis after gamma-irradiation was accompanied by a breakdown of the mitochondrial membrane potential (psi(m)) that was counteracted by growth stimulation. We propose that growth stimulation intercepted p53 proapoptotic signaling at the level of mitochondrial integrity, most likely by upregulating the antiapoptotic factors Bcl-x(L) and Bfl-1. Upregulation of Bcl-x(L) and of Bfl-1 upon growth stimulation was mediated by the PKC-dependent activation of NF-kappaB. Consequently, blocking PKC activity restored apoptosis in stimulated, irradiated splenocytes. The inherent coupling of growth stimulation with antiapoptotic signaling in primary lymphocytes might provide hints as to how precancerous lymphocytes bypass the need for mutational inactivation of p53. Thus, our findings might explain the relatively low frequency of p53 mutations in lymphomas in comparison to other tumor entities.

Leukemia-lymphoma cell lines as model systems for hematopoietic research

Continuous human leukemia-lymphoma (LL) cell lines comprise a rich self-renewing resource of accessible and manipulable living cells which has illuminated the pathophysiology of hematopoietic tumors as well as basic cell biology. The major key advantages of continuous cell lines are the unlimited supply and worldwide availability of identical cell material and their cryopreservation. LL cell lines are characterized generally by monoclonal origin and differentiation arrest, sustained proliferation in vitro with preservation of most cellular features, and specific genetic alterations. The most practical classification of LL cell lines assigns them to one of the physiologically occurring cell lineages, based on their immunophenotype, genotype and functional features. Truly malignant cell lines may be distinguished from Epstein-Barr virus (EBV)-immortalized normal cells, using various operational and conceptual parameters. The characterization and publication of new LL cell lines provides important and informative core data which, by opening new avenues for investigation, have become ubiquitous powerful research tools that are available to every investigator by reference cell repositories. There is a need in the scientific community for clean and authenticated LL cell lines to which every scientist has access as offered by these institutionalized public cell line banks. A list of the most useful, robust and freely available reference cell lines is proposed in this review. Clearly, studies of LL cell lines have provided seminal insights into the biology of hematopoietic neoplasia.

The nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse model of childhood acute lymphoblastic leukemia reveals intrinsic differences in biologic characteristics at diagnosis and relapse

Acute lymphoblastic leukemia cells from 19 children, including 7 who remain in first complete remission (CR1), were engrafted into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. High-level infiltration of bone marrow, spleen, and liver was observed, with variable infiltration of other organs. The immunophenotypes of xenografts were essentially unaltered compared with the original patient sample. In addition, sequencing of the entire p53 coding region revealed no mutations in 14 of 14 xenografts (10 from patients at diagnosis and 4 at relapse). Cells harvested from the spleens of engrafted mice readily transferred the leukemia to secondary and tertiary recipients. To correlate biologic characteristics of xenografts with clinical and prognostic features of the patients, the rates at which individual leukemia samples engrafted in NOD/SCID mice were analyzed. Differences in biologic correlates were encountered depending on stage of disease: a direct correlation was observed between the rate of engraftment and length of CR1 for samples harvested at relapse (r = 0.96; P =.002), but not diagnosis (r = 0.38; P =.40). In contrast, the in vivo responses of 6 xenografts to vincristine showed a direct correlation (r = 0.96; P =.002) between the length of CR1 and the rate at which the leukemia cell population recovered following vincristine treatment, regardless of whether the xenografts were derived from patients at diagnosis or relapse. This study supports previous findings that the NOD/SCID model of childhood ALL provides an accurate representation of the human disease and indicates that it may be of value to predict relapse and design alternative treatment strategies in a patient-specific manner.

Mix-ups and mycoplasma: the enemies within

Human leukemia-lymphoma (LL) cell lines represent important tools for experimental research. Among the various problems associated with cell lines, the two most common concern contaminations: (1) cross-contamination with unrelated cells and (2) contamination with microorganisms, in particular mycoplasma. The bad news is that about one-third of the cell lines are either cross-contaminated or mycoplasma-infected or both. The good news is that there are means to recognize and overcome these problems. In cases where, during attempts to establish new LL cell lines, primary LL cultures are cross-contaminated with continuous cell lines, intended new cell lines simply cannot be established ("early" cross-contamination). In cases of "late" cross-contamination of existing LL cell lines where the intrusive cells have a growth advantage, the original ("uncontaminated") cell lines may still be available elsewhere. DNA fingerprinting and cytogenetic analysis appear to be the most suitable approaches to detect cross-contaminations and to authenticate LL cell lines. A different but related aspect of "false" LL cell lines is the frequent misclassification of cell lines whereby the actual cell type of the cell line does not correspond to the purported model character of the cell line. Mycoplasma infection can have a multitude of effects on the eukaryotic cells which, due to the variety of infecting mycoplasma species and many other contributing parameters, cannot be predicted, rendering resulting data questionable at best. Practical procedures for the detection and elimination of mycoplasma contamination have been developed. Diagnostic and preventive strategies in order to hem the alarming increase in "false" and mycoplasma-positive LL cell lines are recommended.

Detection of p53 gene mutations by single strand conformational polymorphism (SSCP) in human acute myeloid leukemia-derived cell lines

We have identified new mutations in the p53 gene in 3/11 growth factor-independent and in 2/8 growth factor-dependent human acute myeloid leukemia (AML)-derived cell lines by single-strand conformational polymorphism (SSCP) and sequencing analysis. MEG-01 had a triplet deletion at codon 304; F-36P, NB-4 and MV4-11 showed point mutations at codon 344. F-36P had a second point mutation at codon 270 and NB-4 additionally at codon 319. M-MOK had a nucleotide substitution at codon 191. The frequency of p53 mutations in the cytokine-independent cell lines was comparable to that in the cytokine-dependent lines. These results suggest that loss of Wild type (wt) p53 is not the decisive event causing tumor cells to proliferate in vitro without externally added growth factors.

Paradox of Bcl-2 (and p53): why may apoptosis-regulating proteins be irrelevant to cell death?

Although the Bcl-2 family members and p53 are involved in the regulation of apoptosis, the status of apoptotic machinery (eg caspases) plays a major role in determining the mode and timing of cell death. If the apoptotic machinery is lost, inhibited, or intrinsically inactivated, the "death stars", Bcl-2 and p53, may become irrelevant to cell death. In this light, high levels of Bcl-2 may indicate that downstream apoptotic pathways are still functional. This explains why Bcl-2 overexpression can be a marker of chemosensitivity and favorable prognosis in certain cancers and why retention of wild-type p53 may manifest inactivation of caspases in aggressive cancers.

Human cancer cell lines: fact and fantasy

Cancer cell lines are used in many biomedical research laboratories. Why, then, are they often described as unrepresentative of the cells from which they were derived? Here, I argue that they have been unjustly accused. Under the right conditions, and with appropriate controls, properly authenticated cancer cell lines retain the properties of the cancers of origin.

Continuous hematopoietic cell lines as model systems for leukemia-lymphoma research

Along with other improvements, the advent of continuous human leukemia-lymphoma (LL) cell lines as a rich resource of abundant, accessible and manipulable living cells has contributed significantly to a better understanding of the pathophysiology of hematopoietic tumors. The first LL cell lines, Burkitt's lymphoma-derived lines, were established in 1963. Since then, more than 1000 cell lines have been described, although not all of them in full detail. The major advantages of continuous cell lines is the unlimited supply and worldwide availability of identical cell material, and the infinite viable storability in liquid nitrogen. LL cell lines are characterized generally by monoclonal origin and differentiation arrest, sustained proliferation in vitro under preservation of most cellular features, and specific genetic alterations. The most practical classification of LL cell lines assigns them to one of the physiologically occurring cell lineages, based on their immunophenotype, genotype and functional features. Truly malignant cell lines must be discerned from Epstein-Barr virus (EBV)-immortalized normal cells, using various distinguishing parameters. However, the picture is not quite so straightforward, as some types of LL cell lines are indeed EBV+, and some EBV+ normal cell lines carry also genetic aberrations and may mimic malignancy-associated features. Apart from EBV and human T-cell leukemia virus in some lines, the majority of wild-type LL cell lines are virus-negative. The efficiency of cell line establishment is rather low and the deliberate establishment of new LL cell lines remains by and large an unpredictable random process. Difficulties in establishing continuous cell lines may be caused by the inappropriate selection of nutrients and growth factors for these cells. Clearly, a generally suitable microenvironment for hematopoietic cells, either malignant or normal, cannot yet be created in vitro. The characterization and publication of new LL cell lines should provide important and informative core data, attesting to their scientific significance. Large percentages of LL cell lines are contaminated with mycoplasma (about 30%) or are cross-contaminated with other cell lines (about 15-20%). Solutions to these problems are sensitive detection, effective elimination and rigorous prevention of mycoplasma infection, and proper, regular authentication of cell lines. The underlying cause, however, appears to be negligent cell culture practice. The willingness of investigators to make their LL cell lines available to others is all too often limited. There is a need in the scientific community for clean and authenticated high-quality LL cell lines to which every scientist has access. These are offered by various institutionalized public cell line banks. It has been argued that LL cell lines are genetically unstable (both cytogenetically and molecular genetically). For instance, cell lines are supposed to acquire numerical and structural chromosomal alterations and various types of mutations (e.g. point mutations) in vitro. We present evidence that while nearly 100% of all LL cell lines indeed carry genetic alterations, these alterations appear to be stable rather than unstable. As an example of the practical utility of LL cell lines, the recent advances in studies of classical and molecular cytogenetics, which in large part were made possible by cell lines, are highlighted. A list of the most useful, robust and publicly available reference cell lines that may be used for a variety of experimental purposes is proposed. Clearly, by opening new avenues for investigation, studies of LL cell lines have provided seminal insights into the biology of hematopoietic neoplasia. Over a period of nearly four decades, these initially rather exotic cell cultures, known only to a few specialists, have become ubiquitous powerful research tools that are available to every investigator.

Karyotypic dissection of Hodgkin's disease cell lines reveals ectopic subtelomeres and ribosomal DNA at sites of multiple jumping translocations and genomic amplification

Although the neoplastic significance of the chromosome changes widespread in Hodgkin's disease (HD) remains obscure, a distinct cytogenetic picture has emerged combining aneuploidy with structural rearrangements clustered at certain breakpoints. Notably absent are the recurrent chromosome translocations which distinguish other hematopoietic neoplasms and serve as clues to underlying oncogene alterations. The paucity of neoplastic cells in HD biopsies hinders detailed chromosome analysis. As an alternative, we investigated a panel of well characterized cell lines by classical and molecular cytogenetics, using single-gene and subtelomeric probes, including three autologous HD examples (HDLM-1/2/3) analyzed by 'spectral karyotyping' - the first complete HD karyotype to be documented. Although complex, most rearrangements in HDLM cells arose in vivo and included few rare but many typical HD breakpoints, notably at the r(ibosomal)DNA regions. Two types of genomic rearrangement involving DNA repeats were conspicuous: insertion and genomic amplification/coamplification of rDNA-the first genomic rDNA rearrangements to be reported in a tumor cell, and the first example of multiple 'jumping translocations' (JT). Of four subtelomeric microsatellite repeats tested in HDLM cells, three exhibited interstitial sites at JT, of which two (at 5qter and 9pter) were respectively associated with deletion of the 5q31-32 myeloid region, and coamplification of a recently described HD-recurrent amplicon at 9p2 together with transcriptionally silent rDNA. Altogether, three out of four HD cell lines carried interstitial 9p subtelomeres and rDNA rearrangements. Taken together, these data suggest tumorigenic rearrangements may be facilitated by 'hitchhiking' along with mobile DNA repeat sequences which may target gene rearrangement at 9p in HD. Southern analysis of parallel rearrangements within rDNA intergenic spacers in HDLM cells highlighted several at, or near, retroposons. As well as validating HD cell lines as cytogenetic models, and resources for identifying genes rearranged in HD, our findings warrant further investigation of the roles of DNA repeat sequences, notably subtelomeric microsatellites, rDNA spacer sequences and retroposons as facilitators and markers of tumor-gene rearrangement.

Malignant hematopoietic cell lines: in vitro models for the study of natural killer cell leukemia-lymphoma

Malignancies involving natural killer (NK) cells are rare disorders. The complexity of NK cell-involving disorders has only recently been appreciated. Modern classifications discern immature (precursor) from mature NK cell leukemias-lymphomas. Continuous NK leukemia-lymphoma cell lines represent important model systems to study these neoplasms. While there are a number of putative NK cell lines which are, however, either not characterized, not immortalized, non-malignant, non-NK, or plain false cell lines, six bona fide malignant NK cell lines have been established and are sufficiently well characterized: HANK1, KHYG-1, NK-92, NKL, NK-YS and YT. Except for YT which was derived from a not further defined acute lymphoblastic lymphoma, these cell lines were established from patients with various NK cell malignancies. Five of the six cell lines are constitutively interleukin-2-dependent. Their immunoprofile is remarkably similar: CD1-, CD2+, surface CD3 (but cytoplasmic CD3epsilon+), CD4-, CD5-, CD7+, CD8-, CD16-, CD56+, CD57-, TCRalphabeta-, TCRgammadelta-, negative for B cell and myelomonocytic markers. The immunoglobulin heavy chain and T cell receptor genes are all in germline configuration. All six lines show complex chromosomal alterations, with both numerical and structural aberrations, attesting to their malignant and monoclonal nature. Functionally, these cells which contain azurophilic granules in their cytoplasm are nearly universally positive in NK activity assays. Three of five cell lines are Epstein-Barr virus-positive (type II latency). The composite data on these six cell lines allow for the operational definition of a typical malignant NK cell line profile. NK leukemia-lymphoma cell lines will prove invaluable for studies of normal and malignant NK cell biology.

A novel natural killer cell line (KHYG-1) from a patient with aggressive natural killer cell leukemia carrying a p53 point mutation

We present the establishment of a natural killer (NK) leukemia cell line, designated KHYG-1, from the blood of a patient with aggressive NK leukemia, which both possessed the same p53 point mutation. The immunophenotype of the primary leukemia cells was CD2+, surface CD3-, cytoplasmic CD3epsilon+, CD7+, CD8alphaalpha+, CD16+, CD56+, CD57+ and HLA-DR+. A new cell line (KHYG-1) was established by culturing peripheral leukemia cells with 100 units of recombinant interleukin (IL)-2. The KHYG-1 cells showed LGL morphology with a large nucleus, coarse chromatin, conspicuous nucleoli, and abundant basophilic cytoplasm with many azurophilic granules. The immunophenotype of KHYG-1 cells was CD1-, CD2+, surface CD3-, cytoplasmic CD3epsilon+, CD7+, CD8alphaalpha+, CD16-, CD25-, CD33+, CD34-, CD56+, CD57-, CD122+, CD132+, and TdT-. Southern blot analysis of these cells revealed a normal germline configuration for the beta, delta, and gamma chains of the T cell receptor and the immunoglobulin heavy-chain genes. Moreover, the KHYG-1 cells displayed NK cell activity and IL-2-dependent proliferation in vitro, suggesting that they are of NK cell origin. Epstein-Barr virus (EBV) DNA was not detected in KHYG-1 cells by Southern blot analysis with a terminal repeat probe from an EBV genome. A point mutation in exon 7 of the p53 gene was detected in the KHYG-1 cells by PCR/SSCP analysis, and direct sequencing revealed the conversion of C to T at nucleotide 877 in codon 248. The primary leukemia cells also carried the same point mutation. Although the precise role of the p53 point mutation in leukemogenesis remains to be clarified, the establishment of an NK leukemia cell line with a p53 point mutation could be valuable in the study of leukemogenesis.